This invention relates to a process for manufacturing an active carbon formed into a granular or other suitable shapes by using a phenolic resin as a binder.
Recently, demand for active carbon has extended even to the field of desulphurization of smoke exhausted from a boiler and of water treatment, and is rapidly increasing in parallel with the emergent progress of public pollution preventive measures. An active carbon for these uses is required such as can be formed in a granular or other suitable shape having excellent adsorption capacity and erosion resistance in addition to low production cost.
Among granular active carbons supplied so far, there have been available those pillar-shaped ones 2-5 mm. in diameter obtained by an extrusion with tar, pitch, molasses, waste liquor of sulfite pulp or lignin used as a binder, or those of specified standard sizes obtained by merely grinding and sieving e.g., a cocoanut shell active carbon as it is without using any binder. These are all limited in their practicabilities inview of their shapes, dimensions and mechanical strengths and cannot fulfill the requirements for adsorption treatment on a large scale.
A granular active carbon, one typical example of formed active carbons, is packed in a tower to form an adsorbent layer and thus performs the required selective adsorption when gas, vapor or liquid passes through the said layer. In the case of a large quantity treatment, the granular active carbon should have a high adsorption capacity and, at the same time, be able to withstand the heavy weight of stacked layers. Moreover, it should be immediately durable enough to withstand even the wear resulting from its continuous use. It is also desired that the granule itself should be high in density so that the volume of the adsorbent layer in the packed tower, can be small.
Generally speaking, however, if the adsorption capacity of an active carbon is to be increased, it usually requires lowering of its mechanical strength, dimension and density, which so far could not but limit the conventional active carbon considerably in its manufacture and use. That is, it was unavoidable that, if the bulk density of a granule was too high at the granule formation stage, it was difficult to activate the granule, thus lowering its adsorption capacity and if the adsorption capacity was increased at the activation stage, the granular active carbon obtained was necessarily too bulky and unavoidably reduced in mechanical strength. In consequence, there was no alternative but to compromise the mechanical strength and the adsorption capacity at the cost of both properties to some extent.
The object of this invention is to provide a shaped active carbon in a granular or other suitable shape which is excellent both in mechanical strength and adsorption capacity and is, moreover, high in erosion resistance.
This object can be attained by using a one step phenolformaldehyde resin, a furfural-modified phenol resin, or mixtures thereof (these resins are generically referred to as "phenolic resins" hereinafter).